This section is intended to provide a background or context to the invention that is, inter alia, recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
Patterned nanoscale inorganic materials with controllable characteristic feature size, symmetry, and properties are of considerable interest in a wide range of fields. However, as feature dimensions shrink below 50 nm, conventional top-down lithographic patterning methods typically suffer from slow processing speeds and high costs. To date, wide-scale implementation of applications for nanomaterials has been hindered by limitations associated with production. Molecular-level control in the synthesis of nanomaterials with precisely tunable properties is highly desired for mass production of nanoscale devices. Equally important in production is low-cost fabrication of periodic nanoscale features over large areas. Using conventional methods, these twin goals are generally at odds with each other.
An alternative, and less expensive approach, is to employ a process analogous to the biomineralization process and use self-assembled organic structures as growth-directing agents to guide the synthesis of inorganic materials into the desired morphology. For example, block copolymers (BCPs), which have two or more chemically dissimilar homopolymers joined together through covalent bonds, can self-assemble into ordered periodic nanostructure configurations (e.g. spheres, cylinders, lamellae and bicontinuous structures) under appropriate conditions due to microphase separation. Useful devices can be fabricated from ordered block copolymer structures by tuning the material properties of the two polymer domains. Although the properties of the component polymers can be adjusted prior to forming the ordered domains using organic synthesis, this may affect the phase separation of the polymers and prevent formation of the desired nanostructure.
BCPs have offered a relatively easy, inexpensive, and versatile platform for templating inorganic materials growth. A variety of inorganic materials have been self-assembled on BCPs for localized selective growth of such materials in the desired domains, which can act as nanoreactors to physically confine the growth, generally through hydrophobic forces. However, using conventional techniques, the dimensions of the templated materials are determined by the physical size of the original domains in the BCP scaffold, limiting the flexibility of these methods. Moreover, the loss of selectivity from uncontrolled homogeneous reactions cannot be fully prescribed, especially for reactions involving hydrolytic unstable precursors such as titania and other technologically important metal oxides. More importantly, the localized material growth in the targeted domains is not controllable on the molecular level, which is vital for assuring large-scale uniformity in mass production of organized nanoscale materials with precisely controlled material properties.